Field of the Invention
Embodiments of the present invention relate to vehicle seats. More specifically, the embodiments relate to vehicle seats having a headrest that has a portion facing the head of a user which is movable in the vertical direction.
Description of the Related Art
A conventional vehicle seat has a headrest supporting a head of a user. A pad exhibiting an adequate elastic force is packed into the headrest. When, for example, a vehicle is hit from behind (rearward collision), the headrest assuredly supports the head of the user seated in the seat.
A rearward collision may be of various types. For example, in a first type of collision, the user is pressed backwards as shown in FIGS. 13 to 16, and then his body moves upwards. In a second type of collision, the user is pressed backwards as shown in FIGS. 17 to 21, and then his body moves downwards. In a third type of collision, his body moves upwards first, and then moves downwards.
In the case of the first type of collision, the head of the user is supported by the pad of the headrest. However, when his body moves upwards, the head receives a backward rotational force (as indicated by the arrow Rc in FIG. 15). As a result, the user may sustain a whiplash injury. In the case of the second type of collision, the head of the user is supported by the pad of the headrest. However, due to the downward movement of his body, his head receives a forward rotational force (as indicated by the arrow Rd in FIG. 20). As a result, the user may sustain a whiplash injury.
Japanese Laid-Open Patent Publication No. 2008-149862 discloses a technique in which there is provided a tension spring for biasing a movable headrest. The headrest is retained in a position where the headrest is under a biasing force. When a sensor predicts a rearward collision, the biasing force of the tension spring is released by using a solenoid. As a result, the movable headrest moves instantaneously upwards. The headrest moves upwards not at the instant that the rearward collision occurs but at the instant that the rearward collision is predicted. Thus, there is the possibility that the upward movement of the headrest does not coincide with the upward movement of the body of the user.
As a result, in some cases, it is impossible to effectively suppress the backward rotation of the head of the user. The movement distance of the headrest is fixed. Thus, even when the movement of the headrest coincides with the movement of the body, the movement distance of the headrest may be excessive or deficient. As a result, in some cases, it is impossible to sufficiently suppress the backward rotation of the head of the user. In the case where the body of the user moves downwards at the time of collision, ascent of the headrest may aggravate the forward rotation of the head further. A conventional headrest requires a complicated structure for its movement.
Thus, there has been a need for a headrest capable of further reducing burden on a user's neck when the user's body moves at the time of rearward collision. It is more desirable for the headrest to be simple.